Fuel cell power plants are well known and are commonly used to produce electrical energy from hydrogen containing reducing fluid and oxygen containing oxidant reactant streams to power electrical apparatus such as motors, and transportation vehicles, etc. In fuel cell power plants of the prior art, it is well known that fuel cell performance decays over time.
Fuel cell performance decay is due to several related phenomena. One such cause of performance decay is corrosion that takes place on electrodes, and especially on cathode electrodes. Cathode electrodes are exposed to a corroding oxidative environment as a result of the presence of an oxygen rich oxidant fluid within the cathode environment, while anode electrodes are exposed to a non-corroding, reducing environment as a result of the presence of a hydrogen rich reducing fluid fuel within the anode environment. An additional cause of decay arises from reduction of activity of an electrocatalyst making up part of a cathode or anode electrode due to a change in composition of the catalyst resulting from oxidative corrosion or due to recrystalization of the catalyst. Mass transfer characteristics of the cathode or anode electrode structure may be reduced due to oxidation of materials within the electrode that increase the wettability of the electrode. Such oxidation may result in flooding of the electrode with an electrolyte of an aqueous electrolyte, or with product water of a proton exchange membrane (“PEM”) electrolyte. Further, the electrolyte in the fuel cell may become contaminated by reaction, adsorption and absorption of foreign materials, thereby reducing conductivity of the electrolyte. It is known that these performance decay phenomena are generally most severe on the cathode electrode because of the influence of the cathode potential and oxidant on these degradation mechanisms. Therefore, degradation at the cathode electrode leads to significant performance loss of the cathode electrode and the fuel cell.
The amount of catalyst required for the anode or fuel electrode is less than an amount of catalyst required for the cathode or oxidant electrode because the oxygen reduction reaction at the cathode electrode in most known fuel cells is much slower than the fuel oxidation reaction at the anode electrode. Additionally, known fuel cells are frequently designed having a rectangular shape defining a short axis and a long axis. The oxidant reactant stream in such fuel cells is typically passed through the cell in a direction parallel to the short axis, and the fuel reactant stream is passed through the cell in a direction parallel to the long axis of the cell. Such an approach tends to minimize a depth of reactant flow channels and maximizes a number of fuel cells per unit length of a fuel cell stack assembly, which is an important design element. Consequently, efforts to minimize cathode electrode degradation must confront limitations of a traditional, rectangular plan form of known fuel cells. It is desirable, therefore, to develop a fuel cell power plant that minimizes performance decay resulting from degradation of the cathode electrode.